The present invention relates generally to semiconductor fabrication and, more particularly, to a method for controlling airflow on a backside of semiconductor wafer during spin processing and a method for reducing particle recontamination on a backside of a semiconductor wafer during spin processing.
As the semiconductor industry moves to larger, e.g., 300 mm, wafers and to smaller, e.g., 0.18 xcexcm and smaller, feature sizes, it is becoming increasingly more important to control wafer contamination on the backside, i.e., the bottom side, of wafers during wafer preparation operations. In one conventional wafer preparation operation, a wafer is spin rinsed in a spin, rinse, and dry (SRD) module. During this spin rinsing operation, deionized (DI) water is sprayed onto the top side and the backside of a wafer as the wafer is spun at high speed. One problem with this spin rinsing operation is that recirculating air from above the wafer often causes particle recontamination on the backside of the wafer.
FIG. 1 is a simplified schematic diagram 10 illustrating the airflow around a wafer in a conventional bowl, which forms part of an SRD module. As shown therein, wafer 12 is disposed in bowl 14. For ease of illustration, the spindle, which spins the wafer, and the spindle fingers, which support the wafer above the spindle, have been omitted from FIG. 1. As wafer 12 spins in bowl 14, the spinning action of the wafer transfers energy to the air flowing to the top side of the wafer. This transferred energy causes the airflow above the top side of wafer 12 to become turbulent and creates recirculating air, i.e., eddies, as indicated by the arrows in FIG. 1. The amount of energy transferred to the air flowing to the top side of wafer 12 depends on the diameter and the rotational speed of the wafer. In general, the greater the amount of energy transferred to the air, the higher the eddies extend above the top side and the farther the eddies extend below the backside of wafer 12. The presence of eddies below wafer 12 is undesirable because particles or DI water droplets removed from the wafer can circulate in the eddies and be redeposited on the backside of the wafer, thereby causing recontamination.
In view of the foregoing, there is a need for a method for controlling the airflow on a backside of a wafer during spin processing to minimize the recontamination caused by particles and DI water droplets circulating in eddies below the wafer.
Broadly speaking, the present invention fills this need by controlling the airflow on the backside of a semiconductor wafer during spin processing so that contaminated air does not recirculate near the backside of the wafer. The present invention also reduces particle recontamination on the backside of a semiconductor wafer during spin processing by preventing particles from contacting the backside of the wafer.
In accordance with one aspect of the present invention, a method for controlling airflow on a backside of a semiconductor wafer during spin processing is provided. In this method a wafer backing plate is first disposed below a wafer. Air is then supplied to the volume defined by the wafer backing plate and the wafer. In one embodiment, the air is supplied to the volume proximate to the center portion of the backside of the wafer.
The air may be supplied to the volume between the wafer and the wafer backing plate in various manners. In one embodiment, the air is supplied to the volume through a hollow core spindle. In another embodiment, the air is supplied to the volume through a rotary union. In yet another embodiment, the wafer backing plate has a plurality of apertures formed therein and the air is supplied to the volume through the plurality of apertures. In this embodiment, the air supplied to the volume is provided by an air supply system including a plenum disposed below the wafer backing plate, a fan provided with either a HEPA filter or an ULPA filter, and an air duct for channeling air from the fan to the plenum.
The airflow on the backside of the wafer may be controlled by varying the separation distance between the wafer and the wafer backing plate and by varying the flow rate into the volume. In one embodiment, the distance the wafer backing plate is disposed below the wafer is in a range from about 80 thousandths of an inch to about 275 thousandths of an inch. In one embodiment, the operation of supplying air to the volume includes controlling the flow rate of the air supplied to the volume to avoid any substantial recirculation of contaminated air into the volume.
In one embodiment, the speed at which the semiconductor wafer rotates during spin processing is substantially the same as the speed at which the wafer backing plate rotates during spin processing. In one embodiment, the shape of the wafer backing plate substantially corresponds with that of the wafer.
In accordance with another aspect of the present invention, a method for reducing particle recontamination on a backside of a semiconductor wafer during spin processing is provided. In this method a wafer backing plate is disposed below the wafer to prevent particles from contacting the backside of the wafer. In one embodiment, the method is carried out in an SRD module.
The method for controlling airflow on a backside of a semiconductor wafer during spin processing of the present invention advantageously minimizes contamination on the backside of the wafer by preventing contaminated air from recirculating in the volume between the wafer and the wafer backing plate. The method further allows for flexible control of the airflow on the backside of the wafer by varying the flow rate into the volume and the separation distance between the wafer and the wafer backing plate. In addition, the wafer backing plate reduces particle recontamination on the backside of the wafer by preventing particles from contacting the backside of the wafer during spin processing.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.